1. Field of the Invention
This invention relates to an image forming method for printing a variety of information such as images and characters to a recording medium, such as a card, and more particularly to a printing method that is capable of switching printing methods according to the characteristics of the recording medium or the information to print the information.
2. Description of the Related Art
Conventionally, thermal transfer method printing apparatuses that record desired images and characters by thermally transferring with a thermal head via a thermal transfer film to a recording medium are used to create card shaped recording medium, like credit cards, cash cards, license cards and ID cards. As an example, Japanese Patent Publication (Tokkai) No. 09-131930 (U.S. Pat. No. 5,959,278) teaches a direct transfer method printing apparatus that directly transfers images and characters to a recording medium via thermal transfer film. The use of a thermal sublimate ink has the benefit of attaining high quality images because this type of ink is more expressive. However, a receptive layer to receive ink on the surface of a recording medium to which images, etc., are transferred is an essential element to enable this method of printing, so a problem exists in that either the type of recording medium that can be used is limited, or it is necessary to form the aforementioned receptive layer upon the surface of a recording medium.
Generally, cards made of polyvinyl chloride (also known as PVC cards) are widely used as the recording medium because they can receive thermal sublimate ink. However, due to the fact that harmful substances are generated when these cards are burned, there has been consideration given to switching to cards made of polyethylene terephthalate (also known as PET cards). However, PET cards have a crystal-like quality so not only is it difficult to use them for thermal sublimate printing, but embossing them is also difficult. Thus, if it is necessary to emboss the surface of the recording medium, the use of PVC cards is presently unavoidable.
Furthermore, in recent years there are card shaped media of the type having IC chips or antennae embedded therein such as IC cards, which are being used in a variety of fields. Because the embedding of such elements into the card, the surface of the card becomes uneven resulting in problems in transferring images.
Japanese Patent Publication (Tokkai) No. 08-58124 teaches the technology of an indirect transfer method printing apparatus that transfers an image to an intermediate transfer medium once, then transfers that image again to the recording medium, as a method for overcoming the aforementioned problems. According to this method, it is possible to overcome the problems such as the limitation of recording medium related to the receptive layer or the transferring of images to an uneven surface of the recording medium which had been considered demerits of the direct transfer method. Furthermore, this method has the advantage of being easier to printing to the entire surface of the card shaped recording medium compared to the direct transfer method.
In Japanese Patent Publication (Tokkai) No. 11-263032 is disclosed a configuration that establishes a pooling mechanism that functions as a buffer for the transfer sheet between an image forming means that forms images to a belt-shaped transfer sheet (intermediate transfer film) and a re-transferring means that re-transfers images transferred to the transfer sheet to a card that is the target for receiving the image thereby enabling the lining up of the image forming process and the re-transferring process. Disclosed in Japanese Patent Publication (Tokkai) No. 08-58125 is a thermal transfer printing apparatus that prints to both the front and back surfaces of a recording paper, configured to transfer ink to an intermediate transfer film using a thermal head and after forming an image, to re-transfer the ink image to a recording paper surface by a heat roller, and configured to transfer ink to the back side of a recording paper with a thermal head that is different from the aforementioned thermal head, the thermal head for transferring ink to the back surface of the recording paper surface interposed by an ink film is opposingly arranged to a heat roller for the retransfer process.
However, running costs for the intermediate transfer method are higher than the direct transfer method because an intermediate transfer medium must be used. Printing also takes longer. Furthermore, depending on the design of the card, even if the entire front surface is required for printing, often times only the back side is used to print precautions for card use, thus there are fewer cases requiring printing over the entire surface. Thus, it can be said that there are merits and demerits for both methods of printing. Still further, Japanese Patent Publication (Tokkai) No. 11-263032 arranges the image forming process and the re-transferring process lined up adjacently, but it only handles the aforementioned indirect transfer method. Furthermore, to print to both front and back surfaces of a recording medium on the same thermal transfer printing apparatus according to the apparatus disclosed in Japanese Patent Publication (Tokkai) No. 08-58125, it is necessary for the transport speed to be different for the recording medium when being processed by the heat roller or the thermal head. When both surfaces of the recording medium are heated, it has been pointed out that the problem of poor peeling of the film occurs as a result of the high temperature of the intermediate transfer film.
Therefore, to handle information relating to printing, such as the surface shape and characteristics of the recording medium including the type of material of the recording medium such as whether it is PVC or PET, embossed or whether or not it includes IC elements and whether or not it is necessary to print to the entire surface of the recording medium, and the various purposes, if there is an image printing method that can switch printing methods between the direct transfer method and the indirect transfer method to print to a recording medium with either transfer method, convenience to users who are printing would be improved and running costs associated with printing using the optimum image forming method to the recording medium would be reduced.
Also, when forming images to both sides of a recording medium using such an image forming method, generally, private personal information relating to the owner of the recording medium is recorded onto one surface of the recording medium, so from the point of view of security to protect personal information, it is not preferable to form images such as precautions on the other side of the recording medium using the image forming apparatus again after the recording medium having been recorded with personal information on one side has been discharged from the image forming apparatus wherein the aforementioned image forming method was executed, and in the event it is necessary to discharge the recording medium with images formed only on one side from the image forming apparatus for some reason such as an error in a machine failure or power outage, it is preferable to discharge the recording medium with only precautions that does not include personal information printed on one side. To rephrase this, when printing to both sides of a recording medium, providing for the unavoidable discharge of recording medium before printing is completed, without discharging the recording medium from the image forming apparatus until the printing of both sides of the recording medium has been completed, cautions, etc., are formed as images on the recording medium in advance to increase the security to protect personal information by forming images relating to personal information last. Here, security means not only protection of personal information in the image forming apparatus wherein the image forming method is performed normally, but also the protecting of personal information providing for emergency situations in the image forming apparatus.
Furthermore, when switching the image forming method between the direct transfer method and the indirect transfer method to form images to the front and back sides of a recording medium, if after images are formed on one side of a recording medium using the indirect transfer method, images are formed on the other side of a recording medium using the direct transfer method, the fixing of the image transferred in the former image forming on the recording medium will be improved.
When printing (forming images) with a configuration wherein both methods exist inside the printing apparatus, to make the entire printing apparatus more compact and to attain low costs, the sharing of portions of the image forming portion that are used in both methods and when the direct transfer method is selected, the recording medium and the intermediate transfer medium are transported in contact at the image forming position, accompanying the sharing of members. Contact friction of the intermediate transfer medium will be large if the recording medium in contact thereto is moved and the intermediate transfer medium not being used is not transported when using the direct transfer method, resulting in damage to the unused portion of the intermediate transfer medium and thus printing problems in the indirect transfer method.